Copper-silicon-iron alloy



Patented Sept. 10, 1940 UNITED STATES COPPER-SILICON-IRON ALLOY Alan Upson Seybolt, Columbus, Ohio, assignor, by mesne assignments, to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application January 26, 1940, Serial No. 315,751

2 Claims.

The principal object of this invention is to provide a copper-base alloy particularly adapted for use in the manufacture of sound, strong, and hard castings which may readily be machined and polished and which may be forged and otherwise hot-wrought to a limited degree.

There is a large demand for a hard, strong, copper-base alloy having good casting qualities, by which is meant a reasonably low melting point, freedom from segregation, high fluidity even at temperatures only a little above the melting point, substantial freedom from viscous or dry dross during pouring, and soundness when cast. soundness includes freedom from inclusions and from macroscopic gas pockets, shrinkage cavities, and fissures.

With but few exceptions, molten alloys freeze not at a single temperature but overa range of temperatures, and the composition of the part of the alloy which freezes first differs from that which freezes last. Under normal casting conditions, columnar or needle-like crystals are first formed in most alloys, and these crystals are interlaced in a dendritic? structure. Solidificw tion of the interstitial liquid, which is accompanied by shrinkage in volume, often leaves macroscopic porous areas within the metal. Porosity of this type is favored by a wide freezing range and by wide differences in composition of the liquid metal at the beginning and end of freezing. A coarse, open dendritic grain structure in the alloy as castisundesirable because it favors porosity and for other reasons.

In addition to good casting qualities, hard, strong alloys should be readily machinable to a highly polished surface for use in such appli cations as bearings, guides, and printing rolls and plates. Furthermore, it is desirable that the alloy be capable of undergoing at least a moderate amount of forging.

The copper-base alloy of this invention has the desirable properties indicated above in a high degree. Such properties are attained by a novel composition comprising between about 6.5% and a 10.5% silicon, between about 5% and about 15% iron, and the remainder substantially all copper. Preferably, the silicon content is between 7% and 8.5% and the iron between 7% and 12%. If the silicon percentage is above 8.5%, the iron percentage is preferably under 10%.

In alloys of the composition defined above, the first-freezing constituent is apparently an iron-silicon solid constituent. The concentration of this solid constituent is such that, instead of growing to long dendrites, it remains principally as small particles in suspension in the liquid. When the remaining, main bulk of the material freezes, it does so in such a manner as to give a quite uniform dispersion of solid particles in the matrix thereby providing a substantially non-dendritic structure. These alloys may be made by melting copper and adding thereto iron and silicon, or silicon and ferrosilicon, or iron and ferrosilicon, or iron-copper-silicon prealloy. The molten alloy does not seriously attack carbon or clay-graphite crucibles. The small amount of dross formed during melting is easily skimmed from the surface, leaving: a clean-pouring melt having a moderately low melting point.

An alloy containing 7.5% silicon, 10% iron, remainder copper, for instance, starts to freeze at some temperature well above 1700 F., but the constituent so solidifying remains in suspension (probably colloidal) in the liquid. At about 1700 F. the main bulk of the liquid starts to freeze, and freezing is complete at about 1660 F. Such a narrow freezing range is a major advantage in that it fosters homogeneity and soundness of the casting. The alloy of the invention is substantially free from the open dendritic structure often encountered in bronze castings.

The alloys aresufliciently hard and tough for many purposes. For instance, a sand cast 7.5% silicon alloy, quenched in water from l500 F., has a- Vickers hardness (2.5 mm. steel ball, 30 kg. load) between about 120 and about 130 depending partly upon the iron content, and the same alloy when chill cast and quenched in water from 1500 F. has a Vickers hardness between about 130 and 150. In general, the hardness decreases as the iron is raised from 5% to about 10% or 12%, and increases as the iron is raised from about 10% or 12% to 15% or more.-

The Izod impact resistance of the alloys, as measured on a one-inch length of an unnotched bar inch square in cross section, is in the neighborhood of 4 to 8 foot-pounds; their tensile strength is about 44,000 to 50,000 pounds per square inch.

The alloys may be forged, hot rolled, machined, and polished without diificulty.

Corrosion experiments made by immersing 

